1. Technical Field of the Invention
The present invention relates to a steam engine composed in such a manner that a fluid displacement is generated in liquid charged in a tube when vaporization, which is caused by heating the liquid in the tube, and liquefaction, which is caused by cooling the liquid in the tube, are repeatedly carried out.
2. Description of the Related Art
A type of steam engine is conventionally known in which liquid charged in a container is vaporized by heating and liquefied by cooling so as to change the pressure in the container and mechanical energy can be outputted by the change in pressure. This technique is disclosed, for example, in the official gazette of Japanese Patent Unexamined Publication No. 58-57014.
On the other hand, the present applicant applied for patent of the technique of a steam engine having the following constitution. Concerning this technique, refer to Japanese Patent Unexamined Publication No. 2004-84523.
The constitution of this steam engine 500 is shown in FIG. 5.
The steam engine 500 includes: a tube 502 having a substantially U-shaped fluid passage into which liquid is charged; a heater 504 for heating the liquid in the tube 502; a cooler 506 for cooling vapor generated by vaporization of the liquid when it is heated by the heater 504; and an output portion 508.
The output portion 508 includes: a cylinder 510; a piston 512 capable of being reciprocated in the cylinder 510; a movable portion 514, one end portion of which is connected to the piston 512; and a spring member 516 arranged at the other end portion of the movable portion 514.
The piston 512 is reciprocated in the cylinder 510 according to the pressure given by the fluid in the tube 502. Specifically, the piston 512 is reciprocated between a lower end (bottom dead center), which is one end portion on the tube 502 side, and an upper end (top dead center) which is the other end portion on the opposite side to the inside of the tube 502.
In this steam engine 500, when the liquid in the tube 502 is heated by the heater 504 and boiled and vaporized, a volume of the fluid charged in the tube 502 is expanded. Next, the vapor, which has been vaporized being heated by the heater 504, is moved downward and cooled by the cooler 506 and liquefied. At this time, a volume of the fluid in the tube 502 is contracted. When a change in the liquid level (fluid displacement) is caused by the expansion and contraction of the volume of the fluid in the tube 502, the pressure of the fluid is changed and the piston 512 and the movable portion 514 are reciprocated by the change in pressure.
Accordingly, for example, when a permanent magnet is attached to the movable portion 514 and a coil is arranged being opposed to the permanent magnet, an electro-motive force is generated in the coil by the reciprocating motion conducted by the piston 512 and the movable portion 514.
Concerning the steam engine, the present applicant applied for patent of the technique disclosed in the official gazette of Japanese Patent Unexamined Publication No. 2005-330910.
In this connection, in the steam engine 500 shown in FIG. 5, the heater 504 and the cooler 506 are arranged on a tube line, which is formed by the tube 502, at an interval. This portion of the tube 502 corresponding to this interval will be referred to as a connecting tube portion 518 hereinafter, that is, a portion of the tube between the heater 504 and the cooler 506 will be referred to as a connecting tube portion 518 hereinafter.
In the conventional steam engine 500 having the above connecting pipe portion 518, the thermal efficiency is deteriorated.
Explanations are specifically made as follows. First, in this steam engine 500, as shown in FIG. 6, pressure Pm in the connecting pipe portion 518 is repeatedly increased and decreased with the lapse of time and this can be explained as follows.
In the steam engine 500, as the piston 512 is moved from the top dead center to the bottom dead center, a liquid level 520 (shown in FIG. 6) of the liquid piston made by the liquid in the tube 502 is raised from a position close to the cooler 506 to a position (top dead center Lu of the liquid level 520) close to the heater 504. When the piston 512 is moved from the top dead center to the bottom dead center, a volume of the fluid in the tube 502 is reduced. Therefore, as the liquid level 520 is raised, pressure Pm in the connecting pipe portion 518 is raised. Concerning this raise in the pressure, refer to pressure Pm between time t1 and time t2 shown in FIG. 6.
When the liquid level 520 is raised and reaches a height (top dead center Lu of the liquid level 520) of the heater 504 and the liquid close to the heater 504 is vaporized by the heater 504, the fluid volume in the tube 502 is changed being expanded. According to this expansion of the fluid volume, the piston 512 is moved from the bottom dead center to the top dead center. At this time, as shown in FIG. 6, the liquid level 520 is lowered from a position close to the heater 504 to a position (bottom dead center Lb of the liquid level 520) close to the lower end of the cooler 506. When the piston 512 is moved from the bottom dead center to the top dead center as described above, that is, when the liquid piston is moved from top dead center Lu to bottom dead center Lb, the liquid volume in the tube 502 is expanded. Therefore, as the liquid level 520 is lowered, pressure Pm in the connecting tube portion 518 is reduced. Concerning this reduction of pressure Pm, refer to pressure Pm in the period between time t2 and time t4 shown in FIG. 6.
When the liquid level 520 is lowered to the position (bottom dead center Lb of the liquid level 520) close to the lower end of the cooler 506 and vapor, which has been vaporized by the heater 504, exists in a region close to the cooler 506 in the pipe 502, vapor in a region located close to the cooler 506 is cooled by the cooler 506 and liquefied.
When the piston 512 is lowered and starts moving from the top dead center to the bottom dead center at the time of the reduction of pressure Pm, pressure Pm in the connecting tube portion 518 is raised again. When the piston 512 is lowered and the vapor is liquefied by the cooler 506, the liquid level 520 is raised from the position (bottom dead center Lb of the liquid level 520) close to the cooler 506 to the position (top dead center Lu of the liquid level 520) close to the heater 504. Concerning this matter, refer to pressure Pm in the period between time t4 and time t5 shown in FIG. 6.
In this connection, the connecting tube portion 518 is a portion of the tube 502 arranged between the heater 504 and the cooler 506 as described above. Accordingly, temperature Tm of the connecting portion 518 is influenced by the heater 504 and the cooler 506. Therefore, temperature Tm of the connecting portion 518 is a temperature between temperature Th of the heater 504 and temperature Tc of the cooler 506.
In this case, as shown in FIG. 6, pressure Pm in the connecting tube 518 can be changed to be higher or lower than the pressure of saturated vapor Pms of the fluid in the tube 502 at temperature Tm of the connecting tube portion 518.
Pressure Pm in the connecting tube portion 518 is reduced when the liquid level 520 is lowered as described above. In this case, for example, when the liquid level 520 is lowered to a position (bottom dead center Lb of the liquid level 520) close to the lower end of the cooler 506, liquid drops 522 attach onto an inner wall face 518a of the connecting tube portion 518. When pressure Pm in the connecting tube portion 518 is lower than saturated vapor pressure Pms at temperature Tm, the liquid drops 522 are vaporized. Concerning this matter, refer to a change in pressure Pm in the period between time t3 and time t4 shown in FIG. 6.
However, this vaporization of the liquid drops 522 is caused right before the liquid level 520 starts rising from bottom dead center Lb of the liquid level 520. Therefore, this vaporization of the liquid drops 522 seldom takes an action of further lowering the liquid level 520, that is, this vaporization of the liquid drops 522 seldom takes an action of expanding the fluid volume in the tube 502.
Nevertheless, vapor, which is generated when the liquid drops 522 are vaporized, is carried to a portion close to the cooler 506 and cooled by the cooler 506 and liquefied. This means that the vapor, which has been generated when the liquid drops 522 are vaporized, carries heat, which seldom contributes to the expansion of the liquid volume in the tube 502, and forces the cooler 506 to conduct a useless cooling action. Accordingly, in the steam engine 500, a great heat loss is caused by the vapor generated when the liquid drops 522 are vaporized.